Interstitial cystitis (IC) is a chronic inflammatory disease of the bladder for which the etiology is unknown. IC often has a rapid onset with pain, urgency and frequency of urination, and cystoscopic abnormalities including petechial hemorrhages (glomerulations) or ulcers that extend into the lamina propria (Hunner's ulcers).sup.1,2. The rapid onset of IC is followed by a chronic course with partial remissions and re-exacerbations, which can continue for up to 30 years.sup.1,2. As a result of the absence of a specific cause for and lack of understanding of its pathogenesis, there is currently no generally accepted treatment proven to be reliably efficacious.
Various groups have studied IC and speculated as to its cause. Proposed etiologies include infection, allergic or immune disorders, endocrinologic disturbance, toxic urinary chemicals, defective transitional mucosa, psychiatric disorders, neurogenic disorders, lymphatic obstruction, vascular obstruction. Proposed treatments include pentosan polysulfate, anti-inflammatory or immunosuppressant therapy, muscle relaxants, anti-histamines, and analgesics. Of these, only pentosan polysulfate has been approved by the FDA. However, none of the proposed therapies, including pentosan polysulfate, is universally accepted or universally efficacious. As a result, there is a long felt need for adequate therapy of this misunderstood and frequently misdiagnosed disorder.
Certain morphologic and histologic features of IC suggest that the epithelium is usually abnormal in this disease.sup.3-5, with evidence for changes in the bladder mucin layer.sup.6, denudation or thinning of the bladder epithelium and rupture of the mucosa.sup.3-5,7, and intraurothelial infiltration of urinary proteins such as Tamm-Horsfall protein.sup.8. In addition, activation of bladder epithelial cells appears to be abnormal in IC, with altered expression of specific cellular proteins.sup.9. These changes coupled with the chronic nature of IC suggests the possibility of impaired regeneration of normal bladder epithelium. In previous experiments, we discovered a 1-3 kDa peptide in the urine of IC patients that inhibits the proliferation of cultured normal adult human bladder epithelial cells, suggesting that it may be related to the pathogenesis of this disorder (see co-pending application Ser. No. 08/944,202). This peptide is hereafter referred to as the anti-proliferative factor or APF.
The uninjured postnatal urothelium regenerates very slowly, but rapid proliferation of uroepithelial cells in vivo can occur during tissue regeneration in response to injury.sup.10. The limited data that exist for bladder epithelial cells suggest their replication and differentiation are probably influenced by specific paracrine or autocrine growth factors and their regulatory proteins, similar to other types of epithelial cells.sup.10-21. Epithelial cell growth factors known to be present in normal human urine include epidermal growth factor (EGF), insulin-like growth factors (IGF's), insulin-like growth factor binding proteins (IGFBP's), heparin-binding epidermal growth factor-like growth factor (HB-EGF), platelet-derived growth factors (PDGF-A and B), fibroblast growth factors (FGF1 and 2), and transforming growth factor beta (TGF.beta.). EGF, which is produced primarily by cells in the thick ascending limb of Henle and the distal convoluted tubule.sup.22, is present in high concentrations in urine, and can stimulate, but is not required for, mouse bladder epithelial cell proliferation in vitro.sup.23. IGF1 and IGF2 are produced by both kidney and bladder cells and appear to be required for bladder epithelial cell proliferation.sup.10,21,24. The major IGFBP's found in human urine, which can regulate the activity of IGF1 and 2, are IGFBP-2 and IGFBP-3.sup.25. HB-EGF is also known to be produced by human bladder epithelial cells and can stimulate their growth in vitro.sup.26,27. In contrast, current data suggest that the PDGF's, FGF's and TGF.beta. affect bladder epithelial cell migration and/or differentiation, but their role in cell proliferation remains uncertain.sup.10,21.
Exogenously applied growth factors can stimulate epithelial wound repair.sup.11-13. Since IC is histologically characterized by epithelial abnormalities and because the mucosal defects present in IC result in exposure of basal undifferentiated cells and their growth factor receptors to urine growth factors, we reasoned that abnormally low levels of urinary growth factors, such as HB-EGF, that stimulate bladder epithelial cell proliferation could adversely affect bladder epithelial wound repair and be part of the etiology of IC.
We measured urinary levels of HB-EGF in women with IC, asymptomatic control women without bladder disease, and women with acute, self-limited bladder epithelial damage from bacterial cystitis. We discovered that urine levels of HB-EGF are specifically and significantly decreased in the urine of IC patients (see co-pending application Ser. No. 60/051,458). Furthermore, recent data indicate that 1) IC urine contains a low molecular weight anti-proliferative factor (APF) that specifically inhibits HB-EGF production by primary human bladder epithelial cells in vitro and 2) the inhibition of bladder epithelial cell proliferation caused by the APF from IC urine specimens can be blocked by the addition of recombinant HB-EGF to the cell medium.
Based on the above, we have concluded that 1) a low molecular weight factor from IC urine (APF) inhibits HB-EGF production by bladder epithelial cells and 2) HB-EGF may be used as a therapeutic to stimulate bladder epithelial cell proliferation in the presence of the APF, thereby effectively treating IC.